Recently, diverse wireless communication technologies are under development in line with the advancement of information communication technology. Among them, a wireless local area network (WLAN) is a technique allowing mobile terminals such as personal digital assistants (PDAs), lap top computers, portable multimedia players (PMPs), and the like, to wirelessly access the Internet in particular service providing areas such as homes, offices, or aircraft based on a radio frequency technology.
The early WLAN technique supported the rate of 1˜2 Mbps through frequency hopping, spread spectrum, infrared communication, and the like, by using a 2.4 GHz frequency based on IEEE 802.11. Recently, the advancement of wireless communication technology allows supporting of a maximum rate of 54 Mbps by applying orthogonal frequency division multiplex (OFDM) technology and the like to the WLAN. Further, IEEE 802 has developed a wireless communication technique for improving quality of service (QoS), allowing compatibility of access point (AP) protocols, achieving security enhancement, making radio measurement or radio resource measurement, allowing wireless access in vehicular environment, ensuring fast roaming, establishing a mesh network, performing inter-working with external network, performing wireless network management, and the like, and put those techniques into practical use, or are still developing them.
In the IEEE 802.11, a basic service set (BSS) means a set of stations STAs which are successfully synchronized with each other. A basic service area (BSA) means an area including members constituting the BSS. Varied according to propagation characteristics of a wireless medium, the BSA has a somewhat indefinite boundary. The BSS may be classified into an independent BSS (IBSS) and an infrastructure BSS. The former establishes a self-contained network, not allowing an access to a distribution system (DS). The latter, which includes one or more access points (APs) and a DS, generally refers to a BSS in which an AP is used for every communication process including communication between stations.
In an early WLAN communication procedure, the infrastructure BSS does not allow non-AP stations (STAs) to directly transmit data therebetween, requesting that data should go by way of an AP for its transmission. Meanwhile, recently, a direct link setup (DLS) is supported between Non-AP STAs to improve the efficiency of radio communication. According to this, a BSS supporting quality of service (QoS), namely, a QoS basic service set (QBSS) including a QoS station (QSTA) and a QoS access point (QAP) allows the non-AP STAs to set up a direct link and directly communicate with each other via the direct link without passing through the QAP.